Nickel cadmium batteries are important power sources. Batteries of this type are normally sealed and may be used without complicated routine maintenance. The cells may be recharged many times and they provide a relatively constant output potential during discharge.
The nickel electrodes generally comprise a quantity of nickel hydroxide supported by an expanded metal grid or metal screen or a sintered nickel plague. These electrodes generally comprise one or more additives to enhance their performance, e.g., to provide higher efficiency, greater chemical stability and longer cycle life. Many additives have been investigated in hopes of further enhancing the performance of nickel electrodes.
The most commonly used additive is cobalt, which has been found to enhance cycle life, enhance charging efficiency and inhibit electrode growth. Cobalt, however, is becoming more scarce and higher in cost. Thus, some manufacturers have reduced the level of cobalt in their nickel electrodes.
Nickel electrodes may be manufactured by pressing a powder mixture consisting mainly of nickel hydroxide into an expanded metal grid or onto a metal screen. They may also be manufactured by electrolytically depositing nickel hydroxide from a solution of nickel nitrate onto a porous, sintered nickel plaque. U.S. Pat. No. 3,615,830 discloses that the presence of zinc in a pressed nickel hydroxide electrode produces an improvement in charge retention as well as in charge acceptance at elevated temperatures. This improvement is achieved by adding zinc powder or zinc oxide to a mass of dry powders consisting of nickel hydroxide and other powders. After mixing, the powder mixture is pressed into an expanded metal grid to form the pressed powder electrode.
Although U.S. Pat. No. 3,615,830 discloses an improvement in pressed powder nickel electrodes by incorporating zinc therein, the patent does not reveal how zinc might be incorporated into a nickel electrode of the deposited nickel hydroxide type. It is believed that the advantages of incorporating zinc into a pressed powder electrode would not be seen in an electrode of the electrolytically deposited type, because much or most of the zinc or zinc oxide originally present in a porous nickel plaque would be covered over by nickel hydroxide during the electrolytic deposition step.
It is therefore an object of the present invention to provide a process for incorporating zinc into an electrode of the deposited nickel hydroxide type.
It is another object of the present invention to provide an improved electrode of the deposited nickel hydroxide type.
Other objects and advantages of the present invention will be apparent to those skilled in the art upon consideration of the following disclosure.